1. Field of the Invention
This invention relates to an image enlarging or reducing method wherein, from a series of primary image signal components representing an image, secondary image signal components, which correspond to an enlarged image or a reduced image of said image the number of which is different from the number of the primary image signal components, are obtained from interpolating operations. This invention also relates to an apparatus for carrying out the image enlarging or reducing method.
2. Description of the Prior Art
Systems have heretofore been used widely wherein image signals representing images for medical purposes, or the like, are obtained with the X-ray CT, the MRI, or the like, and the images are reproduced as visible images from the image signals with image reproducing apparatuses, such as laser printers or CRT (cathode ray tube) display devices.
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor. As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to radiation which has passed through an object, such as the human body. As a result, a radiation image of the object is stored on the stimulable phosphor sheet. The stimulable phosphor sheet is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored during exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a display device, such as a CRT display device.
Radiation image recording and reproducing systems which use stimulable phosphor sheets are advantageous over conventional radiography using silver halide photographic materials, in that images can be recorded even when the energy intensity of the radiation to which the stimulable phosphor sheet is exposed varies over a wide range. More specifically, since the amount of light which the stimulable phosphor sheet emits when being stimulated varies over a wide range and is proportional to the amount of energy stored thereon during its exposure to the radiation, it is possible to obtain an image having a desirable density regardless of the energy intensity of the radiation to which the stimulable phosphor sheet was exposed. In order for the desired image density to be obtained, an appropriate read-out gain is set when the emitted light is being detected and converted into an electric signal (image signal) to be used in the reproduction of a radiation image as a visible image with an image reproducing apparatus, such as a laser printer or a CRT display device.
In the radiation image recording and reproducing systems described above, when a visible image is reproduced from an image signal with, for example, a laser printer, a visible image is often reproduced which has been enlarged or reduced in accordance with the size of a sheet of film, on which the visible image is to be reproduced, the number of visible images to be recorded on a single sheet of film, or the like. Also, in cases where a visible image is reproduced and displayed on a CRT display device, an enlarged image is often displayed so that details thereof can be observed, or a plurality of reduced images are often displayed so that they can be compared with each other.
In order for an enlarged image or a reduced image to be reproduced, from a series of primary image signal components of an image signal detected from an image, secondary image signal components, the number of which is different from the number of the primary image signal components, are obtained with an interpolating operation. An enlarged image or a reduced image is then reproduced from the secondary image signal components.
When visible images are reproduced with an image reproducing apparatus, such as a laser printer, from various image signals which have been obtained with various different image signal detecting apparatuses, such as X-ray CT scanners and MRI apparatuses, the visible images should be reproduced such that they have suitable sharpness. This is also necessary when visible images are reproduced with an image reproducing apparatus, such as a laser printer, from various image signals obtained from images which were recorded under different recording conditions in, for example, an X-ray image recording apparatus. Such recording conditions include, for example, what portion of an object is represented by the recorded image (e.g., the head, the chest, or the abdomen in cases where the object is a human body) and what mode was used when the image was recorded (e.g., a fluorographic mode, a direct image recording mode, or a contrasted image recording mode).
In order for the visible images having suitable sharpness to be reproduced, several types of interpolation processes have heretofore been prepared with which visible images having different sharpness can be obtained. One of the interpolation processes is selected, and secondary image signal components are obtained with the selected interpolation process from primary image signal components. The secondary image signal components are then used during the reproduction of a visible image.
Even if several types of interpolation processes are prepared in advance, it often occurs that a visible image becomes necessary which has intermediate image quality (sharpness) between visible images capable of being obtained from the prepared interpolation processes. However, with conventional techniques, such a visible image having intermediate image quality could not be obtained. Therefore, even when such a visible image having intermediate image quality is required, a visible image must be selected from those which can be obtained from the prepared interpolation processes and which have image quality different from the desired intermediate image quality.